I recently picked up a used 55gal aquarium from craigslist and am gathering the equipment needed to get it running. I've gotten to the filter and have come to an impasse. I would like to invest in a good canister filter, but don't know much about them. I've seen a number of them say they have the whole three stage filtration, but I always thought that a wet/dry system was better for biological filtration. Many of the canister I've seen look like they have no dry area. So I was wondering if these filters really live up to good three stage filtration like they claim. Thanks

Personally I like the Hang on back style filters for aquariums under 80 gal. But canisters work well . Mechanical filtration in some is achieved through sponge material of different coarsness, biological filtration is achieved with different media designed for that purpose as well as chemical media. These are usually stacked inside the canister with trays or similar type container in such a way as to provide customized filtration . If I were to use a canister I would get one that will move two to three times the volume of water in the aquarium. This would provide plenty of filtration and should you decide on a larger tank in the future you won't get caught with inadequate filtration. Hope some of this is helpful. :)

I use regular flow undergravels on a few of my smaller tanks, but have moved away from them since I've started using sand in my newer tanks. I have a bunch of Tetra Whisper HOB's. I wouldn't spend the money on them new. I have no complaints about them, but for a very similar price you can get a Marineland Penguin model that has the added benefit of the biowheel. I also have a Eheim Liberty HOB filter. I generally like the design of the cartriges but the flow leaves more to be desired. I have a Fluval 204 canister that I have no complaints about just yet, but when reading up on them, someone made a great observation: the input and output of the filter are both on top of the canister, whereas the Eheim canisters have the input at the bottom and the output at the top. This just seems like a no-brainer design choice in terms of reducing media bypass. If I were to buy a brand new canister, it would probably be a Marineland Magnum as I've heard so many great things about them, but so far I have no complaints about my used Fluval.